This invention relates generally to the solar panel art and, more particularly, to an insulated terminal assembly for providing external electrical connection to solar panels.
Solar panels having a plurality of solar cells have in the past been provided with an electrically conductive layer located behind the cell and a terminal assembly having a substantially flat conductive portion connected to the cell and located between the cell and the conductive layer. The electrical connection to the panel is made through terminal posts extending rearwardly from the flat portions and through enlarged openings in the conductive layer. One or more layers of a dielectric pottant material such as polyvinyl butyral provide insulation between the flat portion and the conductive layer. The conductive layer may also be laminated between two sheets of a weatherable dielectric material which are coextensive therewith. This construction has proved satisfactory for panels rated at about 50 volts; however, some panels of this type having higher voltage ratings exhibit low performance characteristics for reasons that have not been well understood. Applicants have discovered that the low performance of these panels in high voltage applications results from an electrical shorting between the edge of the hole cut in the conductive back layer and the flat portion of the terminal. While the provision of dielectric layers between the conductive layer and the flat portion is usually sufficient to prevent shorting at locations remote from the hole, the edge of the hole acts as a line-to-plane source of potential and thus substantially lowers the dielectric standoff through the intervening layers at that location. If a burr exists where the hole is cut in the conductive layer, the burr can act as a point-to-plane source and further lower the dielectric standoff. In high voltage panels, these points of lower standoff can permit arcing or shorting between the conductive back layer and the flat portion of the terminal.
The back layer is transformed from an effective plane source at locations remote from the hole therein to a line or point source at the edge of the hole. The magnitude of the resulting change in standoff provided by intervening dielectric layers can be appreciated by examining the standoff of air in similar situations. Thus, the dielectric standoff of air between two clean parallel plates is approximately 70 volts per mil, while the standoff of air between a point and a plane is on the order of 5 to 10 volts per mil.
A further problem encountered in prior solar panels having conductive back layers is a shorting between the conductive layers and the solar cells themselves. This problem is compounded when the cells are interconnected by a plurality of conductive ribbons which may be deformed at the cut ends thereof in a manner approximating a point source. The dielectric standoff provided by intervening layers is then greatly reduced, increasing the likelihood of a significant leakage current between the back layer and the terminal.
Therefore, in many applications it is desirable to provide a fully insulated terminal structure for effecting external electric connection to solar panels having conductive layers adjacent the backside thereof.